1. Field of the Invention
The present invention relates to a honeycomb structure, and more particularly, it relates to a honeycomb structure which is a catalyst carrier and also functions as a heater when a voltage is applied thereto and which has furthermore an excellent heat shock resistance.
2. Description of Related Art
Heretofore, a honeycomb structure made of cordierite onto which a catalyst is loaded has been used in treatment a harmful substance in an exhaust gas discharged from a car engine. Moreover, it is also known that a honeycomb structure formed by a sintered silicon carbide body has been used in purification of the exhaust gas (see, e.g., Patent Document 1).
An example of such a honeycomb structure is a honeycomb structure including porous partition walls and an outer peripheral wall positioned on an outermost periphery. With the porous partition walls, a plurality of cells extending from one end surface to the other end surface are formed to become through channels of a fluid.
When the exhaust gas is treated the catalyst loaded onto the honeycomb structure, a temperature of the catalyst needs to be raised to a predetermined temperature. However, the catalyst temperature is low at the start of the engine, which has caused the problem that the exhaust gas is not sufficiently purified.
To solve the problem, a method has been investigated which a heater made of a metal is disposed on an upstream side of a honeycomb structure onto which a catalyst is loaded, to raise a temperature of an exhaust gas (see, e.g., Patent Document 2).
Moreover, it has been disclosed that a honeycomb structure made of a conductive ceramic material and including both ends provided with electrodes is used as a catalyst carrier with a heater (see, e.g., Patent Document 3).